Process and bath for electrolytic copper deposition



23, 1955 P, LEENDERS ETAL 3,219,560

PROCESS AND BATH FOR ELECTROLYTIC COPPER DEPOSITION Filed Oct. 12, 1961 X, CONVERSION VERSUS TIME AT H5 |20 F '7. CONVERSION REACTION TIME IN HOURS INVENTORS P5752 LEE/M17526 152w:- zezr 6954/72 ATTORNEYS United States Patent land Filed Oct. 12, 1961, Ser. No. 144,725 6 Claims. (Cl. 204-52) This application is a continuation-in-part of our copending application Serial No. 46,102, filed July 29, 1960, now Patent Number 3,084,112.

The present invention relates to electro-depositing cop per from an aqueous alkaline cyanide copper plating bath and to improved compositions for such baths.

The aqueous alkaline cyanide plating bath serves for copper-striking steel, which cannot be plated with an adherent deposit from an acid bath, the initial plating of zinc die castings, for plating an undercoat of copper before nickel plating and for plating various other base metals. A typical formulation for such baths comprises copper cyanide, potassium cyanide and sodium hydroxide.

spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

It has now been found that these objects can be attained by incorporating in the alkaline cyanide copper plating bath a sugar heptonic acid. As the sugar heptonic acid there can be employed a-heptagluconic acid, [3- heptagluconic acid, nt-manno-heptonic acid, a-galactoheptonic acid, S-galacto-heptonic acid, fructoheptonic acid and rhamnoheptonic acid. Both the D and L forms of the sugar acids can be employed. The sugar acids are normally employed as their alkali metal salts, e.g., sodium heptagluconate and potassium heptagluconate. Even if the free sugar acid is employed, it is converted to the alkali metal salt in the cyanide bath.

These sugar heptonic acids and the alkali salts thereof were disclosed in the copending application Serial No. 46,102 as additives to eliminate staining and other undesirable effects caused by the incorporation of acetylenic brighteners in aqueous alkaline cyanide copper plating baths. We have now found that the sugar heptonic acids may be eifectively used alone as additives.

The preferred sugar acid material is a mixture of potassium a D-heptagluconate and potassium o D-heptagluconate made by reacting D-glucose with potassium cya Among the disadvantages of the cyanide bath is innide and hydrolizing the glucose cyanohydrine.

cluded the accumulation of sodium carbonate, a by- A simplified reaction scheme is as follows:

(3N COOK 000K COOK CHO CHOH JHOH H OH HO H Ed OE +1120 HGOH +1120 H( )OH HO OH HC JOH l +KG l +K I HOCH HOCH HOOH H0 11 HOCH KOH I NH: I HOOH HOOH HOOH H OH HCOH HdoH H J 0H 11d OH Hti OH Hdoii H2013: OHZOH (1112013 CH OH 0112011 D-giucose Glucose- Potassium a-isomer fl-isomer eyanohydrine heptagluconate product of sodium cyanide decomposition, which results This material is identified as potassium heptagluconate in in decreased anode efiiciency. It has been proposed to Example 2. In place of the potassium salt, sodium hepcontrol such accumulation by, for example, freezing out tagluconate can be employed with similar effect. the carbonate through cooling to F. or by precipitation by adding certain calcium salts. However, the freez- Example 1 ing out operation as well as the precipitation methods are cumbersome and expensive. Ingredient Pmmds f Metallic impurities in cyanide baths known to be 1 er harmful include chromium Crt, which reduces cathode Dextrose monohydmte 1 500 399 efiiciency and may result in bhstenng or peeling of any Potassium cyanide 500 133 subsequent plate. The chromium may be reduced with Water) make gallons sodium hydrosulphite, but again, sulphur thereby introdllced into the bath is highly undesirabls- 250 gallons of Water was placed in a tank and the dextrose It is therefore an object of this invention to eliminate monohydmte addad and dissolwd, The potassium the disadvantages normally associated with the use of alid was th dd d together ith enough water to kalins Cyanide pp Plating bathsbring the total volume to 450 gallons. The ensuing re- Amthsl Object of this invention is to eliminate undeaction was slightly exothermic and the temperature rose sirable sodium carbonate accumulation in such baths. l l d i d ithi th range of f g 115 t An additional object of this invention is to increase the 120 F Th i t was i t d d ft b t 90% anode efficiency in such bflthsof the material was converted (determined by titrating A fllfthsl' oblect of this invention is to TedllQe the the free cyanide remaining and/or by calculating the hexfilvalsnt ehfomium Content of alkaline Cyanids pp amount of unreacted dextrose with Fehlings solution) Platlng baths 25 pounds of potassium cyanide was added to speed up It is a still further object of this invention to provide the reaction. When less than 40 grams per liter of unsuch baths having good ehelating and complexing propreacted dextrose was left in the product the solution was erties for most two and three valent metals. heated to boiling for about one hour to hydnolyze the Still further objects and the entire scope of applicaglucose cyanohydrine and to drive off the ammonia. bility of the present invention will become apparent from After cooling to about 170 F. 60 pounds of 35% hydrothe detailed description given hereinafter, it should be gen peroxide was added and the mixture cooled to room understood, however, that the detailed description and temperature and stored.

specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the In the foregoing example the reaction temperature may vary between and F. and the amount of hydrogen peroxide used may range between about 50 and 3 100 pounds of the 35% solution. It is to be understood that sodium heptagluconate may be prepared from dextrose and sodium cyanide and that salts of other sugar heptonic acids may be similarly produced.

As illustrative of the reaction activity in the production of the potassium salt, there is shown in the single figure of the accompanying drawing a curve, the ordinates of which are given in terms of percent conversion of the glucose to glucose cyanohydrine and the abscissae in terms of reaction time in hours. The curve was constructed from values attained in Example 1. The curve was plotted for a reaction time of four hours and slopes sharply at first and then more gradually after a reaction time of about two hours until a 90% conversion value is reached.

Among the outstanding properties of the alkali metal heptagluconates are:

(1) Improved chelating and complexing properties for most two and three valent metals.

(2) Improved effectiveness in anode depolarization.

(3) Brightening effect.

(4) Eifective depression of reverse leveling caused by many primary brighteners.

(5) Ability to reduce hexavalent chromium.

(6) Ability to produce smooth grain refined deposits.

The alkali cyanide copper plating bath can be that in standard operation other than for the above additive. Such baths usually contain from 20 to 75 grams per liter of copper and from 45 to 145 grams per liter of an alkali metal cyanide. While the sugar heptonic acid can be employed in an amount of from 1.0 to 100* grams per liter, it is usually employed in an amount of from 10 to 60 grams per liter.

Typical ranges of materials and conditions are:

Copper cyanide grams/liter 30 to 90 Potassium cyanide .do 45 to 145 Potassium hydroxide do 7.5 to 37.5 pH d0 12 to 14 Temperature F 100 to 175 Cathode current density amperes/ sq. ft" 1 to 80 Anode current density do 1 to 30 Potassium heptagluconate grams/liter 10 to 60 Potassium carbonate do 0 to 110 Rochelle salt do 0 to 45 As a result of the present invention smooth copper electrodeposits are obtained from alkaline cyanide copper plating solutions on conventional base metals such as iron, steel, nickel, lead, copper and alloys, e.g brass. With steel or zinc preferably the base metal is given an initial thin flash of copper from a low eificiency cyanide copper bath.

In the specification and claims, all proportions are by weight unless otherwise indicated.

1n Examples and 3, the anode and cathode efficiencies of baths containing alkali heptagluconates were determined. The plating operations were carried out in a 450 ml. test cell having brass cathodes at a temperature of 150 F.

Wetting agents can be added such as lauryl oxyethylsulphate, nonylphenolapolyethylene oxide, sodium toluene sulphonate, potassium naphthalene bismethylene sulphonate or certain cationic wetting agents.

In the examples, remarkably good anode efficiencies were obtained over a current density range from 2540 amperes/sq. ft. The anode efiiciencies can further be improved if a combination of heptagluconates with other complexing or chelating agents, such as ethylene diamine tetracetic acid or Rochelle salt is used, with the heptagluconate being the main constituent in this combination.

Example 2 Proportions Material: (Pounds) Rochelle salt 170 Sodium benzoate 1 EDTA (40%) 40 Dextrose 9 Potassium heptagluconate (of 50% solution) 730 Water to make gallons.

Example 3 Proportions Material: (Pounds) Sodium benzoate 1 EDTA (40%) 40 Dextrose 8 Potassium heptagluconate (of 50% solution) Water to make 115 gallons.

The materials prepared in Examples 2 and 3 were incorporated in amounts of 5% by weight in plating baths containing:

CuCN oz./gal 8.0 KCN do 1.3 NaOH do 1.8

The results of the efiiciency tests, all of which were run without agitation, are given in Table I.

TABLE I Time Current Percent Percent Temp., (min- Density Additive anode cathode 512 F. utes) (AJEt?) efficiency efiiciency The addition of an alkali metal heptagluconate to an aqueous alkaline cyanide copper plating bath increases the anode efliciency in the solution and gives a smoother copper deposit. This is due to the effect of the heptagluconate of minimizing the roughness-causing films produced by the anodes. In addition, deleterious effects of metallic contaminants capable of interfering with the performance of conventional metallic or organic brighteners are also minimized.

We claim:

1. An aqueous alkaline cyanide copper plating solution consisting essentially of 20 to 75 grams per liter of copper cyanide, 40. to grams per liter of an alkali metal cyanide and 1 to 100 grams per liter of alkali metal salt of sugar heptanoic acid.

2. An aqueous alkaline cyanide copper plating solution of claim 1 wherein said alkali metal salt of sugar heptanoic acid is sodium heptagluconate.

3. An aqueous alkaline cyanide copper plating solution of claim 1 wherein said alkali metal salt of sugar heptanoic acid is potassium heptagluconate.

4. A process for producing a smooth copper electroplate which comprises electroplating copper from an aqueous alkaline cyanide copper plating bath consisting essentially of 20: to 75 grams of copper cyanide, 40 to 145 grams per liter of an alkali metal cyanide and 1 to 100 grams per liter of an alkali metal salt of sugar heptanoic acid.

5. The process of claim 4 wherein the aikali metal salt of sugar heptanoic acid is sodium heptagluconate.

6. The process of claim 4- wherein the alkali metal salt of sugar heptanoic acid is potassium heptagluconate.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Meurant 204-52 Chester 204-52 Leonard 260528 Ceresa et a1. 204-52 Martin et a1 20452 Sperry 260528 6 OTHER REFERENCES Fieser, Organic Chemistry, Reinhold Publishing Corp., 1956, pages 350-351.

Ind. Eng. Chem. (Mehltretter et a1.) 45 :2782 (1953). Lucas Organic Chemistry, 2nd Edition, 1953, American Book C0., pages 613-622.

JOHN H. MACK, Primary Examiner.

Moy 20452 10 MURRAY TILLMAN, Examiner. 

1. AN AQUEOUS ALKALINE CYANIDE COPPER LPLATING SOLUTION CONSISTING ESSENTIALLY OF 20 TO 75 GRAMS PER LITER OF COPPER CYANIDE, 40 145 GRAMS PER LITER OF AN ALKALI METAL CYANIDE AND 1 TO 100 GRAMS PER LITER OF ALKALI METAL SALT OF SUGAR HEPTANOIC ACID. 